Ivor Darreg (May 5, 1917 – February 12, 1994) was a leading proponent of and composer of microtonal or "xenharmonic" music. He also created a series of experimental musical instruments. Darreg, a contemporary of Harry Partch and a close colleague of John H. Chalmers and Erv Wilson, was one of America's leading theorists and practitioners of experimental intonation and experimental instrument building. Frequently he published his writings in his own Xenharmonic Bulletin. Darreg was born Kenneth Vincent Gerard O'Hara in Portland, Oregon. His father John was editor of a weekly Catholic newspaper and his mother was an artist. He dropped out of school as a teenager, but he had both self-taught facility in at least ten languages and a basic understanding of all the sciences. His real love was music and electronics. Because of his choice of music, his father cast him out, and he and his mother set out on their own with little help from anyone. At that point he took on the name "Ivor," which means "man with bow" (from his cello-playing talents) and "Drareg" (the retrograde of "Gerard"), which he soon changed to "Darreg". In the forties, Ivor built an Amplified Cello, Amplified Clavichord, and Electric Organ, the Electric Keyboard Oboe and the Electric Keyboard Drum. The Amplified Clavichord and Electric Organ no longer exist, but the Electric Keyboard Oboe - like the organ, based on blocking oscillator circuits and capable of microtonality -, the Electric Keyboard Drum, which uses buzzer-like relays, and the Amplified Cello are still working. Darreg lived for much of his adult life in or near Los Angeles, California, then spent his final 9 years in San Diego. He coined the term "xenharmonic", designed and built many original microtonal musical instruments, and wrote voluminous amounts of material about various musical tunings. Perhaps his most important contribution to music theory was his idea that different tunings exhibit different "moods".